An insight into the mechanism of the aerobic oxidation of aldehydes catalyzed by N-heterocyclic carbenesElectronic supplementary information (ESI) available: Experimental procedures, mass spectrometric experiments, theoretical calculations and spectra. See DOI: 10.1039/c3cc48929a

N-Heterocyclic carbene catalysis for the aerobic oxidation and esterification of aromatic aldehydes was monitored by ESI-MS (MS/MS) and the key intermediates were intercepted and characterized using the charge-tag strategy. The existence of the key intermediates hypothesized for the N-heterocyclic carbene-catalyzed aerobic oxidation of aldehydes has been proven by ESI-MS (MS) experiments.